1. Field of the Invention
The present invention relates to a scattering module and a backlight module comprising the same and more particularly, the present invention relates to a scattering module structure capable of rendering the brightness of a backlight module more uniform without incurring a non uniform distribution of brightness on a display panel.
2. Descriptions of the Related Art
Liquid crystal displays (LCDs) are full color display devices that utilize the liquid crystal technology with advantages such as low power consumption, low radiation, small footprints, is lightweight and is flexible in size. Therefore, LCDs have been used in many electronic products that incorporate display screens, such as digital cameras, personal digital assistants (PDAS) and TV sets. LCDs differ from conventional cathode ray tube (CRT) display devices in that the liquid crystal layer of an LCD does not emit light by itself. As a result, an additional light source is needed to obtain an image on the screen. Generally, the additional light source is known as a backlight module.
Backlight modules fall into two categories according to the location of the light sources disposed therein: the edge lighting type and the direct lighting type. Generally, direct lighting light sources are the most commonly used type in large-sized backlight modules. The direct lighting type backlight module comprises a plurality of light source devices and a set of optical films. The light emitted from the light source devices is modulated via the optical films and then propagated to a color filter for display on a display panel. Generally, the set of optical films includes one or more layers of brightness enhancement films (BEFs), a diffuser sheet, a diffuser plate and a reflector. A plurality of dot patterns are arranged beneath the diffuser plate, so that when light impinges on the dot patterns, a portion of the light will be transmitted through the dot patterns while the remaining portion is reflected off the dot patterns. By reflecting a portion of the light, an increased number of reflections will occur between the diffuser plate and the back plate. By transmitting the other portion of the light, a dark band prevented from forming above the dot patterns. As a result, a more uniform emergent light beam and thereby an improved overall performance of the backlight module are obtained.
As shown in a cross-sectional view of FIG. 1, a prior art backlight module 1 comprises a set of optical films and a plurality of light sources 11. The set of optical films includes, from top to bottom, a BEF 10, a diffuser sheet 12, a diffuser plate 14 and a reflector 16. The plurality of light sources 11 are disposed on the reflector 16. The light sources may be light emitting diodes (LEDs). Since light emitted from a light source 11 is concentrated in the very front of the light source 11, if the brightness of the light transmitted through the diffuser plate 14 is not uniform, alternate latticed dark and bright streaks or even latticed dark and bright dots tend to arise on the display panel between the individual light sources. FIG. 2 depicts the simulation results of a brightness distribution on a display panel incorporating the backlight module 1. The dark areas as indicated by the ellipse are shown between the individual LED light sources in the display panel. Furthermore, among the current backlight modules of a direct lighting structure, there is a decreased number of light sources as an effort to reduce the cost. In this case, the latticed dark streaks will become more obvious.
To mitigate the latticed dark streaks, a backlight module shown in FIG. 3 has been proposed. As seen in the cross-sectional view of FIG. 3, in order for the light emitted from the light sources to be diffused uniformly, the backlight module 3 has additional dot patterns at the bottom of the diffuser sheet. Accordingly, the set of optical films in the backlight module 3 includes a BEF 30, a diffuser sheet 32, a diffuser plate 34, a plurality of dot patterns 31 and a reflector 36. A plurality of light sources 33 (e.g., LEDs) are disposed on the reflector 36, while the dot patterns 31 are disposed on the bottom surface of the diffuser plate 34. More specifically, the plurality of dot patterns 31 are centered around a point where the light emitting center of the light sources 33 is projected on the diffuser plate 34. By adjusting the size of the individual dot patterns 31 and spacing therebetween in such a way that the linearly density of the dot patterns 31 decreases as the dot patterns 31 are located further away from the central point, the brightness of the light sources 33 is redistributed through the diffusion of the dot patterns 31, thus mitigating the latticed dark streaks arising from a non uniform brightness distribution of the light sources. However, in such a prior art structure, the dot pattern arrangement only takes into account the relative relationships between the individual light sources arranged along the same horizontal or vertical axis, but ignores the fact that the maximum distance between the individual light sources exists in the diagonal direction, thus causing a larger linearly density along the horizontal or vertical axis than that along the diagonal direction. Consequently, when the spacing between the light sources and the interval between the light sources and the diffuser plates are enlarged to a certain extent, the dark areas still arose between the light sources. For example, if LED light sources are used and the spacing between the light sources are enlarged to 26-27 mm while the interval between the LED light sources and the diffuser plates is enlarged to 20 mm, a light transmission plot as shown in FIG. 4 is obtained through an experiment and simulation results. It can be seen from this plot that, although the arrangement of the dot patterns mitigates latticed dark streaks, dark areas still arose between four the LED light sources (as shown by the ellipse).
Accordingly, it is important to provide a new dot pattern arrangement with such a linearly density so that the brightness of the light sources are distributed uniformly in the display panel.